A metallic combustion turbine engine component is typically exposed to a gas temperature that can approach or exceed the safe operating temperature of the component. Coating a component of a metallic combustion turbine engine is a widely used technique for protecting the component from high temperatures. In particular, a common approach to coating a component involves coating the component with a ceramic thermal barrier coating.
To improve efficiency, the firing temperature of a metallic combustion turbine engine continues to be increased. One particular approach to protect a component in an application where the temperature may exceed the safe operating range is to use a ceramic matrix composite (CMC) material.
U.S. Pat. No. 6,197,424, to Morrison et al. and assigned to the assignee of the present invention discloses a turbine engine component fabricated from CMC material and covered by a layer of dimensionally stable, abradable, ceramic insulating material, commonly referred as friable grade insulation (FGI).
Current methods of coating a turbine engine component include the manufacture of an FGI shell. The FGI shell is then used as a tooling substrate onto which CMC is applied, and then thermally treated to form a hybrid CMC article. Typically, in this process, the FGI is cast as a shell within a tool, then dried, removed from the tool, and then partially fired resulting in a structure that can be used as a forming tool onto which CMC can be applied and processed.
Typically, in this process, the FGI is cast to a thickness in excess of the end product and then after the CMC has been applied and processed, the FGI is typically machined to form the final desired thickness. The current process typically requires a single piece FGI casting onto which the CMC will be applied and then fired. This process can be costly, especially if the internal geometry is not a simple cylinder, or is a complex shape.
U.S. Pat. No. 7,311,790 to Morrison et al. and assigned to the assignee of the present invention discloses a ceramic or FGI tile being affixed on a mold or substrate that is formed to define a shape for a passageway. After tiles are affixed to the mold, an outside surface of the tiles is machined to achieve the desired thickness. A CMC layer is then formed over the FGI tiles, the mold is removed, and an inside surface of the tiles is machined to achieve the desired thickness. Gaps between each FGI tile may be left unfilled to accommodate thermal expansion, or they may be filled with a filler material. Nevertheless, further improvements are desirable.